The present invention relates to an image signal encoding/decoding apparatus for effecting data compression of computer display image and for filing or transferring the compressed data and relates to an image signal decoding apparatus for decoding the coded data by said image signal encoding apparatus. The present invention also relates to data coding/decoding system in a binary three primary color facsimile.
Conventionally, image data composed of three primary colors: red (R), green (G) and blue (B) is utilized and treated as it is when memorizing binary color display image on memory medium in a computer or when transferring the image to a remote location through communication network. Namely, when recording or transferring, in the form of bit map pattern, character or graphic display image formed by a computer program or binary color display image obtained from an image scanner, bright and dark signal of R, G and B three primary colors is normally treated by frame-sequential or line-sequential method, typically in CAPTAIN protocol known as one variation of videotex.
When storing and transferring image information, the most dominant technological problem relates to vast quantity of information. For example, an amount of binary color information may reach up to 768,000 bits when composing a single image in a personal computer, containing 640.times.400 number of picture elements, thereby causing increase in memory capacity and transfer time duration. In view of this, conventionally various methods have been proposed for efficient compression of data when handling image information. As such data compression method of binary image information, there has been proposed run-length coding method such as MH and MR represented in recommendation CCITTSG VIII T.6 and widely utilized typically in facsimile machine. However, the run-length coding method is specifically designed for monochrome binary image. No compression method is proposed or practiced for color binary image such as computer display image.